JP5888286B2 - Manufacturing method of bonded wafer - Google Patents

Description

  The present invention relates to a method for producing a bonded wafer using an ion implantation separation method, and in particular, a reproduction obtained by subjecting a separation wafer produced as a by-product when a bonded wafer is produced by an ion implantation separation method to a regeneration process. The present invention relates to a method for manufacturing a bonded wafer by ion implantation separation using a wafer.

  A method for manufacturing an SOI wafer, particularly a method for manufacturing a thin-film SOI wafer capable of improving the performance of advanced integrated circuits, is a method of manufacturing an SOI wafer by peeling an ion-implanted wafer after bonding (ion implantation separation method: smart). A technique called a cutting method (registered trademark) is attracting attention.

  In this ion implantation separation method, an oxide film is formed on at least one of two silicon wafers, and gas ions such as hydrogen ions or rare gas ions are implanted from the upper surface of one silicon wafer (bond wafer), An ion implantation layer (also referred to as a microbubble layer or an encapsulation layer) is formed inside the wafer. After that, the surface into which the ions are implanted is brought into close contact with the other silicon wafer (base wafer) through an oxide film, and then a heat treatment (peeling heat treatment) is applied to form a microbubble layer as a cleaved surface on one wafer (bond wafer). ) In a thin film. Furthermore, it is a technique for manufacturing an SOI wafer by applying heat treatment (bond heat treatment) and bonding firmly (see Patent Document 1). At this stage, the cleaved surface (peeling surface) is the surface of the SOI layer, and an SOI wafer having a thin SOI film thickness and high uniformity can be obtained relatively easily.

  This ion implantation separation method is not limited to a case where a bonded SOI wafer is manufactured through an insulating film, but is also applied to a case where a bonded wafer is manufactured by directly bonding two wafers.

  In this ion implantation delamination method, the bond wafer after delamination (peeling wafer) is subjected to reprocessing (refresh processing) including surface treatment such as polishing and etching again, thereby causing a step generated in the unbonded portion, The surface roughness after peeling and the influence of the implanted residual layer are reduced or eliminated, and the wafer can be used repeatedly. With respect to this regeneration processing method, for example, as in Patent Document 2, a method is proposed in which chamfering and polishing are combined to remove the influence of an ion implantation residual layer existing in the chamfered portion.

  Regarding the regeneration processing performed on the peeled wafer, Patent Document 3 describes that the polishing margin of the peeled wafer surface is set to 2 μm or more, and the peeled wafer is repeatedly reused as a bond wafer. Patent Document 4 describes that polishing of about 5 μm can be repeated up to 10 times in repeated reuse of a peeled wafer. Furthermore, Patent Document 5 describes that the polishing margin of the peeled wafer surface is 1 to 5 μm or more, and that the peeled wafer is reprocessed many times.

JP-A-5-211128 JP 2001-155978 A JP 2008-21892 A JP 2006-140445 A JP 2007-149907 A

  When the film thickness distribution of the SOI layer of the bonded SOI wafer manufactured by the ion implantation separation method is measured, the film thickness unevenness of the marble pattern may be seen. This film thickness unevenness is also observed visually when visual inspection of the SOI layer surface after the bond wafer is peeled off, and the film thickness unevenness forms a pattern in mm units.

  In recent years, the standard of the thickness distribution of the SOI layer has become strict, and it is important to eliminate the film thickness unevenness having a large pattern generated at the time of peeling. In particular, for a variety of SOI layer film thickness of 30 nm or less called ETSOI (Extremely Thin SOI), such film thickness unevenness has a great influence on the manufacturing yield. It is desired.

  The present invention has been made in view of the above-described problems, and suppresses unevenness in the thickness of a marble pattern generated in a thin film when a bonded wafer is manufactured by an ion implantation separation method. The object is to produce a high bonded wafer.

  In order to achieve the above object, according to the present invention, an ion-implanted layer is formed by ion-implanting at least one kind of gas ions of hydrogen ions and rare gas ions on the surface of a bond wafer. After bonding the implanted surface and the surface of the base wafer directly or through an insulating film, a thin film is formed on the base wafer by applying a heat treatment to peel off part of the bond wafer with the ion implanted layer. In the method for manufacturing a bonded wafer, the thickness of the bond wafer and the base wafer is measured before bonding the bond wafer and the base wafer. A combination of the bond wafer and the base wafer that is less than 5 μm is selected and bonded. Method for producing a bonded wafer, wherein the door is provided.

  With such a bonded wafer manufacturing method, it is possible to suppress the film thickness unevenness of the thin film and to manufacture a bonded wafer with high film thickness uniformity.

At this time, as the bond wafer and / or the base wafer, a reclaimed wafer that has been subjected to recycle processing accompanied by thickness reduction is applied to the peeled wafer produced as a by-product when the bonded wafer is produced in the method for producing a bonded wafer. Can be used. This reclaimed wafer can be one that has been subjected to reclaiming with the above-described thickness reduction twice or more, or one that has been subjected to a thickness reduction of 5 μm or more as the reclaiming with the above-mentioned thickness reduction.
The present invention can be suitably applied to such a regenerated wafer that tends to cause film thickness unevenness in particular, and a bonded wafer with high film thickness uniformity can be manufactured while reducing costs.

Further, the bond wafer and the base wafer can be made of a silicon single crystal wafer, the insulating film can be made of a silicon oxide film, and the thin film can be an SOI layer.
In this way, it is possible to manufacture an SOI wafer with high uniformity of the thin film of the SOI layer.

  In the bonded wafer manufacturing method of the present invention, the thickness of the bond wafer and the base wafer is measured before bonding the bond wafer and the base wafer, and the difference between the thicknesses of both wafers is less than 5 μm. Since a combination to be a wafer is selected and bonded, the film thickness unevenness of the thin film can be suppressed, and a bonded wafer with high film thickness uniformity can be manufactured.

It is a flowchart of an example of the manufacturing method of the bonded wafer of this invention. It is a figure which shows the typical example of the SOI wafer without the film thickness nonuniformity of Example 1-5. It is a figure which shows the typical example of the SOI wafer with the film thickness nonuniformity of the comparative example 1-5.

Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.
In general, when a bonded SOI wafer is manufactured by an ion implantation separation method, for the purpose of cost reduction, the regenerated processing with a reduction in thickness is performed on the separation wafer produced as a by-product when the bonded wafer is manufactured. The wafer is often used as a bond wafer or a base wafer. Alternatively, an unused wafer (a wafer that has not been reprocessed, hereinafter referred to as a prime wafer) may be used as the bond wafer and the base wafer.

As described above, when a bonded SOI wafer is produced by the ion implantation delamination method, there is a problem that uneven thickness of the marble pattern occurs in the SOI layer of the bonded SOI wafer, and the inventors investigated in detail, The following was found.
When prime wafers are used as the bond wafer and the base wafer, the occurrence frequency of unevenness in the thickness of the SOI layer increases when both wafers are manufactured in different manufacturing lots. When a recycled wafer is used as at least one of a bond wafer and a base wafer, the occurrence frequency of film thickness unevenness is higher, and the frequency of occurrence tends to increase as the number of times of regeneration increases. Therefore, the inventor conducted the following experiment using a prime wafer and a recycled wafer, and considered the tendency of the occurrence frequency to increase as follows.

  Generally, the wafer thickness of a silicon single crystal wafer used as a bond wafer and a base wafer is manufactured with a standard of ± 15 μm. Actually, in the same production lot, the thickness variation between wafers is accurate to about ± several μm. Therefore, the use of prime wafers manufactured in the same manufacturing lot is unlikely to cause film thickness unevenness. On the other hand, when the production lots are different and the median thickness of the wafers is shifted, even between prime wafers, the difference in thickness between both wafers may exceed 5 μm, resulting in film thickness unevenness. Increases frequency.

  When a recycled wafer is used for at least one of the bond wafer and the base wafer, the wafer is thinned by a thickness reduction process, and therefore, the possibility that the difference in thickness between both wafers exceeds 5 μm increases. In particular, when a prime wafer is used as one of the bond wafer or the base wafer and a recycled wafer is used as the other, this possibility is very high. Therefore, the frequency of occurrence of film thickness unevenness is also increased.

(Experiment)
As a bond wafer and a base wafer, four types of mirror-polished wafers made of a silicon single crystal having a thickness of 300 mm and a crystal orientation <100> having the thicknesses shown in Table 1 were prepared. For the wafer thickness, the entire surface of the wafer was measured using a capacitance type measuring device, and the average value (rounded off after the decimal point) was adopted.

  These four types of wafers were used as a bond wafer and a base wafer, respectively, and bonded SOI wafers were produced by an ion implantation separation method under the following manufacturing conditions. Thereafter, the thickness of the SOI layer was measured (measuring device: Acumap manufactured by KLA-Tencor) to evaluate the presence or absence of film thickness unevenness. The results are shown in Table 2.

The bonded SOI wafer manufacturing conditions at this time are shown below.
[Conditioning SOI wafer manufacturing conditions]
(Oxide film) A 55 nm thermal oxide film is formed on the bond wafer, the base wafer has no oxide film,
(Hydrogen ion implantation conditions) Injection energy: 48.7 keV, dose amount: 5 × 10 ¹⁶ / cm ² ,
(Peeling heat treatment) At 350 ° C. for 4 hours + 500 ° C. for 30 minutes, Ar atmosphere,
(Planarization heat treatment) Thickness of SOI layer to about 70 nm by sacrificial oxidation treatment at 1200 ° C for 1 hour in Ar atmosphere (SOI film thickness adjustment)

From the results in Table 2, it was found that when the difference in thickness between the bond wafer and the base wafer is 5 μm or more, the film thickness unevenness of the SOI layer occurs. Here, ○ in Table 2 represents that no film thickness unevenness occurred, and x represents that film thickness unevenness occurred.
The mechanism of how the difference between the thickness of the bond wafer and the base wafer is related to the occurrence of film thickness unevenness is not clear, but when the thickness is different, the peeling area has a unique area when peeling. This is presumed to be due to the different frequencies.

  As described above, the present inventors have found that the occurrence of film thickness unevenness is caused by the large difference in thickness between the bond wafer and the base wafer, and have completed the present invention.

Hereinafter, the manufacturing method of the bonded wafer of this invention is demonstrated, referring FIG.
In the present invention, as a bonded wafer having a thin film on a base wafer, for example, an SOI wafer in which an SOI layer is formed on a silicon single crystal wafer via a silicon oxide film can be manufactured.

  First, as shown in FIG. 1A, a bond wafer 10 and a base wafer 11 are prepared. At this time, a combination of a bond wafer and a base wafer having a thickness difference of less than 5 μm, more preferably 3 μm or less is selected from a plurality of wafers whose thicknesses have been measured in advance. This selection step may be performed before the step of bonding the bond wafer and the base wafer, and is not particularly limited in the order of execution with respect to other steps before the bonding step. For example, the selection step may be performed after the step of forming an ion implantation layer on the bond wafer described below.

  In this way, if a combination of a bond wafer and a base wafer having a difference in thickness between the two wafers of less than 5 μm is selected and bonded as described later, the occurrence of film thickness unevenness of the thin film can be suppressed after peeling. A bonded wafer with high film thickness uniformity can be manufactured.

  Here, a prime wafer or a recycled wafer can be used for both the bond wafer and the base wafer. Alternatively, a prime wafer can be used for one of the bond wafer and the base wafer, and a recycled wafer can be used for the other. Incidentally, the reclaimed wafer is a wafer obtained by subjecting the peeled wafer produced as a by-product when the bonded wafer is produced as described above to a rework process accompanied by a reduction in thickness. If the reclaimed wafer is used, the cost can be reduced. Therefore, it is preferable. In particular, reclaimed processing with thickness reduction was performed twice or more, that is, reclaimed wafers that were reused twice or more, or reclaimed wafers with thickness reduction of 5 μm or more as reclaimed processing with thickness reduction, Conventionally, even if a recycled wafer that tends to cause film thickness unevenness of the thin film is used, the film thickness unevenness of the thin film can be suppressed according to the bonded wafer manufacturing method of the present invention.

  Next, as shown in FIG. 1B, an oxide film 12 to be a buried oxide film 16 is grown on the bond wafer 10 by, for example, thermal oxidation or CVD. Alternatively, the oxide film 12 formed at this time may be formed only on the base wafer 11 or may be formed on both wafers. When manufacturing a directly bonded wafer, this oxide film does not need to be formed.

Next, as shown in FIG. 1C, at least one kind of gas ion of hydrogen ions and rare gas ions is implanted into the bond wafer 10 from above the oxide film 12 by an ion implanter. An ion implantation layer 13 is formed. At this time, the ion implantation acceleration voltage is selected so that the target thickness of the peeled silicon (thin film 15) can be obtained.
Next, as shown in FIG. 1D, the ion-implanted bond wafer 10 is adhered and bonded to the base wafer 11 so that the implantation surface is in contact.

  Then, the bonded wafer is held at 350 ° C. to 500 ° C. and subjected to a heat treatment for generating a microbubble layer in the ion implantation layer 13 and is peeled off by the microbubble layer, and a base as shown in FIG. A bonded wafer 14 having a buried oxide film 16 and a thin film 15 formed on the wafer 11 is produced.

Note that the bonding strength of the wafers adhered at room temperature can be increased by performing plasma treatment on the surfaces to be bonded in advance and bonding them.
Then, as shown in FIG. 1 (j), the bonded wafer 14 can be subjected to planarization heat treatment, bonding heat treatment, polishing, or the like to flatten the peeled surface or increase the bonding strength.

  In the above manufacturing process, as shown in FIG. 1E, a peeled wafer 17 which is the bond wafer 10 after peeling is by-produced. The separation wafer 17 has a step portion that has not been transferred to the base wafer 11 on the outer peripheral portion of the separation surface 18. Such reclaimed processing for removing the stepped portion of the peeled wafer 17 can be used as a reclaimed wafer at the time of manufacturing the next bonded wafer. The reclaiming process of the separation wafer 17 can be performed as follows, for example.

  First, as shown in FIG. 1F, the oxide film other than the oxide film on the surface opposite to the peeled surface 18 is removed by cleaning with, for example, an HF aqueous solution. Thereafter, the peeled surface is polished to flatten the peeled surface and remove the damage layer caused by ion implantation, as shown in FIG. Thereafter, as shown in FIG. 1 (h), the back surface oxide film 12 is removed by performing HF cleaning such as a normal batch type HF liquid bath immersion method, and the same surface and back surface quality as the prime wafer are obtained. A reclaimed wafer can be produced. By this reclaiming process, the thickness of the reclaimed wafer becomes thinner than that of the original bond wafer.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.

(Example 1-5, Comparative Example 1-5)
A bonded SOI wafer was prepared using a mirror-polished wafer made of a silicon single crystal having a diameter of 300 mm and a crystal orientation <100> as a bond wafer and a base wafer, and the presence or absence of occurrence of film thickness unevenness in the SOI layer was evaluated. Table 3 shows the types, thicknesses, and regeneration conditions of the bond wafer and the base wafer used in Example 1-5 and Comparative Example 1-5. The regeneration condition indicates the number of times the wafer has been used as a recycled wafer so far as the number of times of regeneration, and the amount of polishing in the regeneration polishing process as the amount of regeneration polishing. In the example, a combination of those having a thickness difference between the bond wafer and the base wafer measured in advance of less than 5 μm is selected and bonded.

Table 3 shows the results of film thickness unevenness. Here, ○ in Table 3 indicates that no film thickness unevenness occurred, and x indicates that film thickness unevenness occurred. As shown in Table 3, film thickness unevenness did not occur in any of Examples 1-5, whereas film thickness unevenness occurred in any of Comparative Examples 1-5. FIG. 2 shows a representative example of the SOI wafer of Example 1-5 where no film thickness unevenness occurred, and FIG. 3 shows a representative example of the SOI wafer of Comparative Example 1-5 where film thickness unevenness occurred.
Further, the SOI film thickness range (the value obtained by subtracting the minimum value from the maximum value of the in-plane film thickness) of the wafer of Comparative Example 1-5 in which the film thickness unevenness occurred was about 1.5 to 2.5 nm. On the other hand, the SOI film thickness range of the wafer of Example 1-5 having no film thickness unevenness was as good as about 1.2 to 1.8 nm.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.
For example, in the above description, a case where a bonded SOI wafer is manufactured through an insulating film is described. However, the present invention can also be applied to a case where a bonded wafer is manufactured by directly bonding two wafers. .

10 ... Bond wafer, 11 ... Base wafer, 12 ... Oxide film,
13 ... ion implantation layer, 14 ... bonded wafer, 15 ... thin film,
16 ... Embedded oxide film, 17 ... Release wafer, 18 ... Release surface.

Claims (4)

At least one kind of gas ion of hydrogen ion or rare gas ion is ion-implanted on the surface of the bond wafer to form an ion implantation layer, and the surface of the bond wafer and the surface of the base wafer are directly or insulated from each other. A bonded wafer manufacturing method for manufacturing a bonded wafer having a thin film on the base wafer by attaching a heat treatment and separating a part of the bond wafer with the ion-implanted layer after bonding through a film In
As the bond wafer and / or the base wafer, using a reclaimed wafer that has been subjected to a regenerating process accompanied by a reduction in thickness, to a peeled wafer produced as a by-product when the bonded wafer is produced in the method for producing a bonded wafer,
The bond wafer and the base wafer are made of a silicon single crystal wafer,
Before bonding the bond wafer and the base wafer, measure the thickness of the bond wafer and the base wafer, and select the combination of the bond wafer and the base wafer in which the difference in thickness between the two wafers is less than 5 μm. And then bonding them together. A method for manufacturing a bonded wafer. The method for producing a bonded wafer according to claim 1 , wherein the reclaimed wafer is obtained by performing reclaiming with the thickness reduction twice or more. The method for producing a bonded wafer according to claim 1 or 2 , wherein the reclaimed wafer has been subjected to a thickness reduction of 5 µm or more as a reclaim process involving the thickness reduction. The method for manufacturing a bonded wafer according to any one of claims 1 to 3 , wherein the insulating film is made of a silicon oxide film, and the thin film is an SOI layer.

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